Flotation recovery of molybdenite



Dec. 29, 1953 M, BARKER ETAL 2,664,199

FLOTATION RECOVERY OF MOLYBDENITE Filed Aug. 27, 1952 cap/#EAP conci/vnun- Fmm/A//NG N52 ph' 7.0-8.0 Jal/5 (0% AT TORNE Y Patented Dec. 29, 1953 FLOTATION RECOVERY OF MOLYBDENITE Lyle M. Barker, Clifton, and Orel E. Young,

Morenci, Ariz., assignors to Phelps Dodge Corporation, New York, N. Y., a corporation of New York Application August 27, 1952, Serial No. 306,638

12 Claims.

This invention relates to the seperation of molybdenite (MoS2) from ores also containing suldes of other metals. More particularly, this invention relates to the separation of molybdenite from notation concentrates containing molybdenite and" suliides of other metals, particularly iron and copper. f

The major source of metallic molybdenum is from molybdenite. Molybdenite occurs most frequently associated with sulfides of other metals, such as copper and iron, and is recovered With these other sulfides by concentration processes. Because the molybdenite commonly occurs in low concentration in these ores, it is only a minor constituent of the copper-iron concentrates, and its recovery presents a major problem. The present invention represents an eliicient, simple and economical solution of this problem.

It has been recognized that the collector reagents such as organic thiophosphates or xanthates, commonly used for producing the copper concentrates, leave a residue in the concentrates which interferes with subsequent recovery of molybdenite by the usual flotation methods. To

obviate this diiculty, such concentrates containing olF/bdenite have bef-n subieeted to a roasting or steaming treatment before the molybdenite is recovered. Such heating treatments are expensive and impractical unless the tonnage to be treated is relatively small and rich in molybdenite. Also, even under the best conditions, considerable amounts of molybdenite are lost and the efciency of molybdenite recovery is not as high as would be desirable.

A molybdenite concentrate must contain a very high proportion of MoSz and no more than small amounts of copper and other values in order to be usable directly and without further processing in the production of molybdenum. For example, a molybdenite concentrate must contain at least 85% M052 and less than 1.5% Cu in order to be considered high grade.

It is. a primary @feiert nf this ihren-tien to provide a method whereby high grade molybdenite concentrates can be obtained directly and eiliciently by notation treatment of a copper concentrate without any preliminary roasting, steaming or heating.

A further object is to provide such a method in which only inexpensive reagents are used to float the molybdenite selectively.

Another object is to provide such a 'flotation procedure for producing high grade molybdenite concentrates' from copper concentrates containing as little as 0.25% of MoSz, and Still achieve a high efficiency or percentage recovery of the molybdenite in the originalmaterial processed.

Other objects and advantages of the invention will be apparent from the disclosure which follows and from the flow sheet in the appended drawings.

In the drawings,

Figure l is a now diagram of the preferred process of the invention.

Figure 2 is a now diagram showing the countercurrent notation cells used in the final cleaner notation step.

We have discovered that copper concentrates containing relatively large amounts of copper and iron sulldes and low amounts of molybdenite can be processed directly by flotation methods without any preliminary chemical or heat treatment to obtain a high grade molybdenite concentrate. Furthermore, over '70% of the MoSz in the original copper concentrate can be recovered in this form, and the only reagents required are a ferrocyanide and sodium cyanide in -addition to an acid, such as sulfuric acid, where pI-.l adjustments are necessary.

The initial copper concentrate which is processed may have been obtained by using the conventional thiophosphate or xanthate collector and frothing agents, and may contain as little as 0.25%, or even less, of MoSz, with 25% or more each of Cu and Fe in the form of a mixture of sulfides.

The process ofkour invention consists essentially of a rougher flotation and several cleaning stages during which an iron cyanide compound is used as reagent, and a final cleaning with an alkali metal cyanide. Throughout the procedure, the pH is careiullycontrolled and adjusted where necessary by acid addition, and the pulp density is controlled and varied from stage to stage. rihe tailing from the rougher notation contains most of the copper values and becomes the copper concentrate that goes to the copper smelter. The concentrate from the rougher notation contains the bulk of the molybdenite and gradually upgraded as it progresses through the various cleaning stages until the final high grader molybdenite concentrate is obtained from the last cleaning operation. The tailings rfrom the iirst'cleaner flotation are returned to the feed for the rougher flotation, While the tailings from later ,cleaning stages are returned to other points in orderto provide a closed circuitoperation.

The copper concentrate may be used as just as it comes from the` copper concentration plant. .Such a :concentrate usually has a high pI-I and contains the residues from additions of lime, collector and frothing agent, during the flotation treatment of the original ores. Water and acid are added in a conditioner to adjust the pH to about '7.0 to 8.0 and the pulp density to about 17% to solids. The conditioner may consist of any suitable tank or container in which the pulp is kept under agitation. The pulp is then fed by any suitable distributor into one or more rougher flotation cells and the reagent, preferably sodium ferrocyanide, is added as the pulp enters these cells. The reagent addition raises the pH of the pulp somewhat so that ithasa pH of about '7.5 to 8.5 during .the rougher flotation.

The concentrate from the rougher flotation then passes through several cleaner flotation stages with the pulp adjusted before each stage to a lower density. The concentrate in 'each case is diluted when necessary in a conditioner .to vthe requisite pulp density fand where necessary its ApH.is again adjusted in the conditioner to .about `.'T;0 'to l8;0 before each addition of 'ferrocyanide After several Vsuch cleaner stages-operating with pulp densities of about '10 to 14%, the concentrate is thickened, filtered, regroundin aba'll mili or the'like and again cleaned. One or more cleaner notations may be used after -regrinding .and are ,preferably carried out with sodium ferrocyanide reagent at a lower ypulp density than .in `the earlier cleaning stages. At fthisstageit is prefn erable to use a pulpdensty of the order of 2 to 3% solids and the pH may run higher, preferably in the range of about 7.5 to 9.0.

'I'he concentrate thus obtained still contains excessive amounts of copper suliides and vis subjected to a nal cleaning with sodium .cyanide .reagent at a -substantially .higher pH, .such as 9.0 to 11.5. The sodium cyanide is alkaline enough to raise the pH of the vvpulp .to this range without addition of .other reagents. This final cleaning appears to bemost .effective Ain .depresw .ing covellite, while the earlier cleaning operations depress andseparatemost of the .chalcocite rand some of the covellite,

We .have found .that although commercial sodium ferrocyanide is .ideal for .use as a reagent in Athe rougher fiotationand following cleaner flota- Vtionsbecause of .its lowcost, other watersoluble .iron cyanide compounds such .as thealkaliearth terrocyanides -or ferricyanidesmay be usedin the nal cleaning stage in place of sodium ferrocyanide.

The number of iron cyanide cleaning stages -employed will depend, ofcourse, on .the .composi- .tion lof the copper concentrate to be processed, including the amount .of molybdenite .contained linitand the :amount andnature of theassociated copper and iron suliides. .'Also, if desired, Athe process can be simplifiedsomewhat at the expense of efficiencyin the molybdenite recovery.

The equipment usedin the ,different operations 'can be conventional flotation cells such .as the standard Fagergren, Denver or Jetair cells, and'it is convenient to arrange them in banks as will be readily understood by those skilled .in the art. vWe have also found that theefect of the iron cyanide, such assodium ferrocyanide, diminishes with time so that itis desirable to .add this reagent to the pulp asit goes into theflotation icells, inorder'to obtain maximum effectiveness. "This is particularly important in the rougherflotation landthe earlier cleaner "flotations The'pH adjustments mustbemade to'provide'the proper pH 'duringthe actual flotation operations. This can be done most easilybyadding acid as necessary preferably around 10%. ferrOCyanide, preferably rcarried out after rein a conditioner tank, the amount of acid added being dependent upon the alkalinity of the materials flowing into the conditioner in each case. The pH of the pulp in these conditioners is not critical but must be adjusted to make allowance for the effect on pH produced by the addition of reagent as -the pulp from the conditioner fiows vinto the flotation cells.

Residual frothing agents in the copper concentrates may cause trouble in the rougher and earlier cleaning flotations by creating excessive froth in thecells. We have found, however, that this .can .be controlled adequately by one or two thickening operations followed by dilution with -frother-free water. Residual collector reagents in the pulp do .not appear to interfere with the recovery of molybdenite by our process.

lThe pulp densities found preferable are as follows; The rougher flotation is carried out at pulp density of about 20% solids. If the solids con- .tent 'is .substantially below 17% at .this stage, the coarser particles-of the `pulp tend to settle and .disrupt the pulp flow. .If the solids exceed v25%, vfrothing .may become excessive `and too muchof the copper and iron sulfides will becar- -riedover into the molybdenite concentra-te. These limits may not be critical, however, for all cop- .per'concent-rates, but will yvary somewhat .depending on the yiineness of the initialconcentratefeed .and the vamount of residual f-rother contained vin it.

YFor the first cleaner notation, a much lower pulp density is desirable. We have found theta `solids content of about -12 to 118% and preferably a1ound.l4% is best forthis-rstor primary'clean- Subsequentcleaningoperations may be'calried out at a pulpdensity of about 8 to 12% :solids The last cleaning with .grinding to liberate .Ymolybdenite attached to ,sangue materials, ris carried out at 1a :still llower adensity. In thiscase, a pulp density of about 2 rto 3% solids is best and it may be necessary to addsome-irothing-agent:such as methyl isobutyl .carbinol1 or the like, because of the preceding thickening and filtering. The 4pulp Vvdensity :then

.doesnot have to be changddffor'the `final cleaning with alkali cyanide.

While other'standardfequipmentimay be used, we have foundthat the 'Denver'type mechanical flotation cells work very Well `for these last two cleaning stages when .the pillnislow'in solids.

In order to disclosefmoreiclearly .the-nature'of the present invention, the followingspecic example illustrating the typical preferred exemplication of the process will hereinafter' be -deF scribed. Itshould lne-understood, however, that this ,is `done solely by way of example and is intended neither to ydelineate the -scope ofthe invention Vnor limit the lambit of .the appended claims.

Example The following is an example of ,our Vprocess as applied to a vcopper concentrate vobtained `from a .copper ore mined in Morenci, Arizona. The concentrate is produced from ,the .original ore by an .initialflotation using lime, organic thiophosphate and a standard .nothing agentas the reagents. Our process begins with this copper ccncentrate, which may Contain approximately 0.25 molybdenite, together .with .copper and. iron sulfides in .amounts assayine about '25 to 530% each of copper and (iron.

We first prepare the copper concentrate for a `rougher flotation by transferring the concentrate to a conditioning tank where the pH of the solution is lowered to 7.0 to 8.0 by addition of sulfuric acid. Copper concentrates usually have a higher pH well in the alkaline range of 10.0 to 12.0. The

.pH may be adjusted by the use of any acid but we prefer the mineral acids because of their low cost and availability. For our operations, we prefer the use of sulfuric acid. However, any acid which is not unduly oxidizing in nature is satisfactory.

In this first conditioner, the pulp density is adjusted by adding water to a concentration of total solids in the range of between 17 to 25% solids,

preferably around 20% solids.

Just prior to introducing the conditioned concentrate pulp into rougher flotation cells, a quantity of a solution of sodium ferrocyanide is added. We find it desirable to make the addition of the sodium ferrooyanide at the feed inlet of the first cell of each of the flotation banks, or to the pulp distributor which supplies a flow of pulp from the conditioner tank into the flotation cells.

The ferrocyanide is added in an amount which will permit some flotation of copper and iron sulf'ldes at the last flotation cell in each bank so as to obtain maximum flotation and recovery of the molybdenite. We have found that a desirable amount of sodium ferrocyanide for the rougher flotation stage is about 0.33 pound of the reagent per ton of original copper concentrate treated.

The conditioned concentrate or pulp and reagent are fed into a bank of flotation cells, preferably of the mechanical agitation type such as the standard Fagergren cells. The number of cells will depend, of course, on the volume and tonnage of concentrates to 'be treated. These cells are connected in series.

The tailings from this rougher flotation which are high in copper content are collected and subjected to thickening to remove excess amounts of Water. The thickened tailings are filtered and the processed copper concentrate thus obtained is sent to the smelter for production of metallic copper.

The concentrate from the rougher flotation step (with a molybdenite concentration of perhaps 1.35%) is mixed with tailings from the fourth and na1 cleaning operations and goes to a thickener, such as a Dorr-type thickener, to remove excess quantities of water containing frothing agent. introduced into a second conditioning tank where further sulfuric acid is added to adjust the pH to between 7.0 and 8.0 and water is added to reduce the pulp density to around 14% total solids.

The pulp from this second conditioner is then introduced along with a solution of sodium ferrocyanide in an amount of approximately 0.24 pound of reagent per ton of original copper concentrate into another bank of flotation cells,

where the first or primary cleaning operation is performed. The concentrate from this primary cleaning flotation step (which may now contain approximately 10% molybdenite, 45% copper'and 12% iron) is prepared for several subsequent flotation steps by transfer to a third conditioning tank. The tailings from the primary cleaner are recycled to the first conditioning tank.

One conditioning is suitable for the next two cleaner flotation steps. In this third condition- The thickened material is then ving tank, the pH is adjusted again with sulfuric acid to lower the pH range to 7.0 to 8.0 and the solids are reduced to around 10% by the addition of more water. Further sodium ferrocyanide is added simultaneously with the introduction of the pulp from this third conditioner into another bank of flotation cells. A suitable amount of sodium ferrocyanide is in the order of .071 pound per ton of original copper concentrate. The concentrate from this secondary flotation step then goes directly into another bank of flotation cells where the tertiary cleaning operation is carried out. Another portion of ferrocyanide is added to the feed of the tertiary cleaners, the amount usually being the same as used for the secondary cleaning. At the end of the tertiary cleaning step, the molybdenite in the concentrate has increased to approximately 30% and the copper and iron have diminished to approximately 31 and 9%, respectively. The tailings from the secondary and tertiary cleaning operations are combined and returned to the second conditioning tank.

Prior to conducting the fourth or quaternary cleaner flotation step, we find it advantageous to subject thel concentrate to a regrinding in order to effect an optimum separation and recovery of the molybdenite. The concentrate from the tertiary cleaning is first thickened to remove a large percentage of the agents which have been concentrated by the preceding flotation steps. Also, the thickening removes a large part of the water in the concentrate and prepares the concentrate for filtration and subsequent grinding in a ball mill. We find that frequently the molybdenite is attached to, or connected with. gangue material. If this gangue material is not freed from the molybdenite particles, the molybdenite is either lost during subsequent treatment, or if it is recovered, it carries gangue material with it, resulting in undue contamination of the final product.

The ground concentrate is diluted With fresh water to produce a suspension containing approximately 2.5% total solids, and sufficient acid is added to adjust its pH to within the range of 7.5 to 9.0 after sodium ferrocyanide addition. If necessary, frothing agents may be added at this time. A suitable frothing agent is methyl isobutyl carbinol, although many others known to the art may be used satisfactorily. We prefer to use the Denver type flotation cell at this stage', although other type cells may be used satisfactorily. Sodium ferrocyanide solution in the amount of 0.385 pound per ton of original copper concentrate is added simultaneously with the introduction of the pulp into a bank of flotation cells constituting the fourth or Quaternary cleaning. The tailing from the fourth cleaner stage, as mentioned above, is returned and mixed with the rougher concentrate going to the thickener preceding the first cleaner stage. The concentrate from the fourth cleaner stage may be passed directly without any treatment orfaddi- Vtionof reagents to a bank of flotation cells conl,iron suldes contained "in the concentrate.

have found thats. water-soluble-cyanideis necesremoval of the residual amounts of copper and We prefer the use of :sodium cyanide but the other adkali-.metal cyanides are equally satisfactory. Forthis nal .flotation step, We 'again -obtain best .results with the Denver vtype flotation cells but we iind that .in order to obtain maximum utility `8 Ation step which is almost entirely `molybdenite may then be suitably filtered, dried and stored for subsequent recovery of molybdenum -or marketed as desired.

illustrating the quantitative aspects of the process described in the foregoing example showing the analysis of the feed, tailing and concentration 'at different stages of the operation ls Table I which follows:

Table I Feed, percent hFailing, percent Concentratcfpcrcent MOS Cu Fc MGS: Cu Fc MOS; Cu Fe .Roughing 25. 52 28.0 0.144 25.58 27.5l 1. 348 40.58` 19.5 Primary Cleanin 40.58 10.5 0. 933 40.87 19.0 10.100 44.00 12.2 Second Cleaning. 44.60 12.2 3.244 49.93 12.4v 14.950 43.28 11.0 'Third Cleaning ....U. 14.950 43. 28 11.0 .555 51.03 11.2 w00 31.41 0:4 FourthandFiltliCleanings- 29.90 31.4.1 '9.4 l 0-1 39.70 12.6 '50m 18.04 4.3 Final Cleaning.K .1 59.20 18.6-1 4.3, ...70 34.58 6.7 85.23 0.70 3.0

for the sodium cyanide it is advisable to conduct the .flotation using counter-current flow. This Also, examining the `results from a plant applying a flow sheet, such as that ofthe example,

procedure vis shown in :Figure of the drawings 5 as to the assays and distribution oi molybdenite, where the ow of rn. terials is illustrated by the vdiagram. The concentrate from .the fifth cleaner vflotation is added'to the tailing being introduced copper and iron'in v'the feed, -Final concentrate and tailing, we have round the following t0 be the results:

Table II i l l Assays Distribution, percent weicht,

percent i g M082 Cu Fe MoSg Cu I FL l I x l l 0. 331 l 25. 51 E. 6 100. 00 100. 00 i100. 00 0. 100 I 2li. 5S 25. 7 30.12 '09. Gil 9i). 98 s?. Azo I o. 54 1.5 nu. ss .ci ,f .n2

l l i `diluted by the addition of the water rintroduced i with theeoncentrate from the fth cleaner flotation cells. -It sessential for maximum depression of vthe copper and iron suldes which lhave escaped depression in the preceding operations that the -ilnal concentrate flow inthe direction of the i richest concentration of the sodium cyanide. It will be observed that by lthis process, maximum efficiency is had of the more expensive sodium cyanide reagent. The amount of sodium cyanide added may vary. However, for optimum results, we find that a fairly concentrated solution of approximately 0.75 pound of sodium cyanide per ton of original 'copper concentrate is most satisfactory.

The final 'flotation step using the sodium cyanide produces a concentrate having in the range of 85% or 'more molybdenite and with .greatly diminished amounts of copper and iron, these being in the order of 1.5% and 3.0%, or less, respectively. We have obtained consistently by this process in one operation a molybdenite concentrate 'containing 85 to 90% molybdenite and less than 1% Cu with a recoveryof more than -70% of the total MoSz in the voriginal feed.

The concentrate produced from the nal flota- These data show a ratio of concentration oi.' 3737.4 tohavebeen obtained.

The total reagent requirements for this opera- -tionper ton of copper concentrates treated were:

TabZe IIfI Reagent Lbf'ffer Sulfuric Acid 3. l2 Sodium Ferrocyanide.. 1.098

Sodium Cyanide .l

The terms and expressions which wehave employed are used as terms of description and not of limitation, and we have no intention, in the use of such terms and expressions, of excluding any equivalents of the features shown and described or portions thereof, but recognize that various modifications are possible within the scope of the invention claimed.

What is claimed is:

1. A process for recovering molybdenite directly from a notation concentrate containing a small amount of molybdenite and larger amounts of sulfides of other metals, such as copper and iron, which comprises; subjecting said concentrate to a succession of flot-ations with a watersoluble, iron-cyanide compound in a mildly alkaline medium, and to a final dotation with a water-soluble cyanide in a strongly alkaline medium.

2. A process for recovering molybrienite from a notation concentrate containing a small amount of molybdenite and larger amounts of suldes of other metals, such as copper and iron, which comprises; subjecting said concentrate to a succession of flotations at a pH between '7.5 and 8.5 with a water-soluble, iron-cyanide compound, and to a final notation at a higher pH with a water-soluble cyanide.

3. A process for recovering molybdenite from a flotation concentrate containing a small amount of molybdenite and larger amounts of copper and iron sulfides, which comprises; subjecting said concentrate to an initial notation at a pH of between 7.5 and 8.5 with the addition of a water-soluble, iron-cyanide compound, thereafter a plurality of flotation cleaning operations with successive additions of iron-cyanide reagent, and to a final fiotation with a watersoluble cyanide at a pH above about 9.0.

4. A process for recovering molybdenite from a fiotation concentrate containing a small amount of molybdenite, and larger amounts of copper and iron sulfides, which comprises; subjecting said concentrate to a rougher notation at a pH of about 7.5 to 8.5 with the addition of sodium ferrocyanide, subjecting the rougher concentrate to several cleaner flotations with additions of sodium ferrocyanide, and subjecting the concentrate from the last cleaner fiotation to a final cleaner flotation at a pH of about 9 to 11.5 with the addition of sodium cyanide.

5. A process as defined in claim 4 in which the ferrocyanide reagent is added to the pulp irnmediately prior to its entrance into flotation cells.

6. A process as defined in claim 4 in which the pulp density in the rougher notation is of the order of 17 to 25% solids and is lowered during the cleaner notations.

7. A process as defined in claim 4 in which the pulp density in the rougher flotation is of the order of 17 to 25% solids, in the earlier cleaner flotations is of the order of 8 to 18% solids, and in the nal cleaner notation is of the order of 2 to 3% solids.

8. A process for recovering molybdenite from a copper fiotation concentrate containing a small amount of molybdenite and larger amounts of copper and iron sulfides, which comprises; subjecting said concentrate without further treatment to a rougher flotation at a pulp density of 17 to 25% solids and at a pH of between 7.5 and 8.5 with the addition of a water-soluble ironcyanide reagent, subjecting the rougher concentrate at a lower pulp density but at the same pH to at least one cleaner flotation with further addition of the iron-cyanide reagent. and subjecting the cleaner concentrate to a further cleaner flotation with addition of a water-soluble cyanide at a pH of between 9.0 and 11.5.

9. A process for recovering molybdenite from a copper flotation concentrate containing a small amount of molybdenite and larger amounts of copper and iron sulfides, which comprises; subjecting said concentrate to a rougher flotation at a pulp density of about 17 to 25% solids and a pH of about 7.5 to 8.5 with the addition of a water-soluble, iron-cyanide compound subjecting the rougher concentrate to a plurality of cleaner flotations at a pulp density of about 8 to 18% solids and a pH of about 7.5 to 8.5 with further additions of iron-cyanide reagent and subjecting the cleaner concentrate to a further cleaning at a pH of 9 to 11.5 and pulp density of about 2 to 3% solids with addition of an alkali cyanide.

10. A process as defined in claim 8 in which the cleaner concentrate is dewatered, reground and repulped before the final cleaner flotation.

11. A process as defined in claim 8 in which the tailings from all cleaner notations are recycled to earlier stages of flotation to provide a closed circuit operation.

12. A process as defined in claim 8 in which *i the molybdenite concentrate is subjected to counter-current flow in the cyanide cleaning notation so as to be treated last in the most concentrated cyanide solution.

LYLE M. BARKER. OREL E. YOUNG.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,102,738 Greenway July 7, 1914 1,429,544 Stevens Sept. 19, 1922 1,950,537 Barthelemy Mar. 13, 1934 2,620,068 Allen et al. Dec. 2, 1952 FOREIGN PATENTS Number Country Date 607,385 Great Britain Aug. 30, 1948 OTHER REFERENCES Taggart, Handbook of Mineral Dressing, copyright 1945, by John Wiley & Sons. Inc.; New York city, section 12, pp. 27, 28 and 110. 

1. A PROCESS FOR RECOVERING MOLYBDENITE DIRECTLY FROM A FLOTATION CONCENTRATE CONTAINING A SMALL AMOUNT OF MOLYBDENITE AND LARGER AMOUNTS OF SULFIDES OF OTHER METALS, SUCH AS COPPER AND IRON, WHICH COMPRISES; SUBJECTING SAID CONCENTRATE TO A SUCCESSION OF FLOTATIONS WITH A WATERSOLUBLE, IRON-CYANIDE COMPOUND IN A MILDLY ALKALINE MEDIUM, AND TO A FINAL FLOTATION WITH A WATER-SOLUBLE CYANIDE IN A STRONGLY ALKALINE MEDIUM. 